In absorbent articles such as disposable diapers, sanitary napkins and incontinence pads, absorbent materials using as constituent materials hydrophilic fibers such as pulp and water-absorbing resins have been widely utilized for the purpose of absorbing body fluids.
In recent years, these absorbent articles have become more functional and thinner that an amount of water-absorbing resins used in each sheet of an absorbent article, or a proportion of water-absorbing resins in the whole absorbent body, which include water-absorbing resins and hydrophilic fibers, tends to increase. This means that, reducing hydrophilic fibers, which have a smallbulk specific gravity, allows to use water-absorbing resins in large amount, which have an excellent water absorbency and a high bulk specific gravity, the proportion of water-absorbing resins within absorbent bodies increases, reducing a thickness of the absorbent articles without lowering an amount of water absorption.
Therefore, when various absorbent articles including disposable diapers, for instance, are produced using water-absorbing resins, a large amount of water-absorbing resins with high moisture absorbency had to be incorporated into fiber base materials. Thus, there has been a growing problem that, depending on the working environment and climate conditions, resin particles may cause blocking in a hopper or in the middle of a production line, or may adhere to the apparatus, causing to hinder stable production.
As a means for securing fluidity or liquid permeability (SFC or GBP) of a water-absorbing resin at the time of moisture absorption, the following are known: a technology of adding a water-insoluble metal phosphate having a particle size of several micrometers (μm) to several dozen micrometers (μm) to a water-absorbing resin (Patent Literatures 1 to 3); a technology of adding fine silica particles or clay such as kaolin (Patent Literatures 4 and 5); a technology of adding a metal soap (Patent Literature 6); a technology of adding a surfactant (Patent Literature 7); a technology of adding an organic polysiloxane (Patent Literature 8); a technology of adding an aluminum salt (Patent Literatures 9 to 11); a technology of adding a polyamine compound (Patent Literatures 12 to 15) and the like.